In the fabrication of integrated circuit chips, vacuum-operated devices are used for the handling of individual semiconductor articles. Such devices typically include a vacuum-actuated tool and a replaceable wand tip having a pocket in vacuum communication with the tool. In operation, the surface of the wand tip associated with the vacuum pocket is brought into contact with the wafer, so that the wafer is maintained against the surface until the vacuum pressure is released.
Handling of a semiconductor wafer or chip should be performed swiftly, but carefully. Typically, a valving mechanism is contained within the handling tool. The most common valving mechanism is one in which a user presses a reciprocating button or lever to cause displacement of a valve stem. The valve stem is a cylindrical member having a circular groove cut into the outside surface. The valve stem may be biased into a position in which the circular groove is aligned with an axial bore of the tool, thereby allowing fluid communication between the forward portion and rearward portion of the axial bore. A force which overcomes the bias displaces the circular groove relative to the axial bore, restricting air flow from the forward portion to the rearward portion of the axial bore.
One difficulty with the valving mechanism described above is eliminating any leakage through the axial bore when the circular groove on the valve stem is misaligned with the axial bore. The valve stem is slidably fit within the tool. Using tight tolerances to fit the valve stem within the tool minimizes leakage around the valve stem from the forward portion to the rearward portion of the axial bore. However, a tightly fit valve stem requires significant force to move the circular groove from an aligned position to a misaligned position. Over time, the repeated actuation of a tight-tolerance valving mechanism will cause discomfort to a user. An alternative is to provide a valve stem which is less tightly fit into the tool. However, this loose fit permits significant air flow from the forward portion to the rearward portion of the axial bore. At the forward portion of the axial bore is the tip which is connected to the electronic article to be relocated. Ideally, the actuation of the valving mechanism eliminates vacuum pressure at the tip and the electronic article is released. However, leakage about the valve stem results in a reduced, but potentially significant, vacuum pressure at the tip. The reduced vacuum pressure will slow the release of the electronic article and for lightweight articles, such as integrated circuit chips, the remaining vacuum pressure may even prevent release.
U.S. Pat. No. 4,767,142 to Takahashi et al. teaches a valving mechanism which reduces the problem caused by leakage around the valve stem. A bypass passageway is provided to link the forward portion of the axial bore to the atmosphere surrounding the tool when vacuum pressure is to be cut off by movement of the valve stem. While the Takahashi et al. device is an improvement over the prior art, the device remains susceptible to leakage about the valve stem. Unless the device is manufactured utilizing close tolerances, leakage still occurs around the valve stem to the rear portion of the axial bore. This leakage may slow the release of an integrated circuit chip. Moreover, the Takahashi et al. device is susceptible to a second leakage along the surface of the valve stem. The second undesired leakage is to the atmosphere during pickup operation of a wafer or integrated circuit chip.
It is an object of the present invention to provide a vacuum-actuated tool for handling electronic articles, wherein the tool insures effective and immediate release of an article with comfortable manipulation by a user.